A start-stop system automatically shuts down and restarts an engine in a vehicle while the vehicle is not in motion to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. A start-stop system can be beneficial for vehicles which spend large amounts of time waiting at traffic lights or frequently come to stops in traffic jams. Start-stop systems are often found in conventional engine-driven vehicles or hybrid electric vehicles (HEV).
FIG. 1 illustrates a known start-stop system 100. Start-stop system 100 includes a main battery 102 connected to a secondary battery 104 through a DC/DC converter 106. The main battery 102 is connected to a starter motor 108 and an auxiliary load 110. The starter motor 108 is coupled to an engine 112. The secondary battery 104 is coupled to a generator motor 114 through a DC-to-AC inverter 116. The generator motor 114 is coupled to the engine 112.
Main battery 102 provides power to start motor 108 to start engine 112 from a cold start (i.e., after the user has turned off engine). Secondary battery 104 provides the necessary power for the generator motor 114 to start the engine 112 after a temporary stop. If there is insufficient charge in secondary battery 104 (e.g., providing 48 VDC), secondary battery 104 may be charged from main battery 102 (e.g., providing 12 VDC) via DC/DC converter 106.
In order for start-stop system 100 to function properly, additional circuitry may be required. For instance, a voltage stabilizer (not shown) may be necessary to maintain the voltage of the main battery 102 so that devices in the auxiliary load 110 can perform during start-stop operation. Furthermore, additional pre-charge and bypass circuits (not shown) may be required in order to store energy in the secondary battery 104. This arrangement adds cost to the system. Moreover, the DC/DC converter 106 is a conversion stage that may not provide sufficient power capability.
Thus, there is a need for a more efficient start-stop system.